WASHINGTON — A worrisome culture of fear that made launch officers believe they had to get perfect test scores to be promoted fueled a widening cheating scandal within the military’s nuclear missile corps, according to Air Force officials.

Half of the 183 launch officers at Malmstrom Air Force Base in Montana have been implicated in the cheating investigation and suspended, signaling deeper morale and personnel problems in a force critical to America’s nuclear security.

Air Force Secretary Deborah Lee James said the scandal hasn’t affected the safety or reliability of the military’s nuclear mission. Speaking to Pentagon reporters Thursday, James and Lt. Gen. Stephen Wilson, who heads the Global Strike Command, said that so far it appears the cheating was confined to the Montana base, even while a climate of frustration, low morale and other failures permeates the nuclear force, which numbers about 550.

The cheating scandal is the latest in an array of troubles that now have the attention of senior defense officials, including Defense Secretary Chuck Hagel. The Associated Press began reporting on the issue nine months ago and revealed serious security lapses, low morale, burnout and other problems in the nuclear force. The Air Force recently announced the cheating scandal, which grew out of a drug investigation.

“These tests have taken on, in their eyes, such high importance, that they feel that anything less than 100 could well put their entire career in jeopardy” even though they only need a score of 90 to pass, said James, who recently took over as secretary. “They have come to believe that these tests are make-it-or-break-it.”

The launch officers didn’t cheat to pass the test, “they cheated because they felt driven to get 100 percent,” she said.

Of the 92 officers implicated so far, as many as 40 were involved directly in the cheating, Wilson said. Others may have known about it but did not report it.

Separately, James said that an investigation into drug possession by officers at several Air Force bases now involves 13 airmen, two more than initially announced. The drug probe led to the discovery of the cheating problem, when investigators found that launch officers were texting answers to each other.

All 92 officers — nearly 17 percent of the force — have been decertified and taken off the job while the scandal is being investigated. That means other launch officers and staff must fill in, performing 10 24-hour shifts per month, instead of the usual eight, Wilson said. Staff members from the 20th Air Force, which oversees all of the nuclear missile force, are also being tapped to do the shifts.

The Air Force has 450 intercontinental ballistic missiles, or ICBMs, on alert at all times. Each day, 90 officers work in pairs inside 45 underground launch control centers, with each center monitoring and controlling a group of 10 ICBMs. They work 24-hour shifts in the missile field and then return to their base.

The latest scandal set off a top-level search for solutions, including a round of visits by James to all the nuclear bases, where she met privately with small groups of airmen to get their insights into the problems.

James and Wilson said that the problems underscore the need to develop new testing and training procedures, provide more incentives and rewards for those who perform well, and set up a system that looks at more than test scores when evaluating officers.

Officials have yet to discipline any commanders or officers beyond those who actually took the tests. But the ongoing reviews look at leadership and accountability within the force. That includes a culture of poor integrity that may encourage officers to share test answers as a way of looking out for each other.

“I do believe there are climate issues, and part of that will be assessing commanders — how did this happen?” said James.

Wilson said all missile launch officers have now been retested, and the average score was about 95 percent. He said 22 failed. Additional nuclear testing and crew evaluations are also being done.

Malmstrom Air Force Base is responsible for 150 Minuteman 3 nuclear missiles, or one-third of the entire Minuteman 3 force. The other two bases are F.E. Warren in Wyoming and Minot in North Dakota.

The tests in question are designed to ensure proficiency by launch officers in handling “emergency war orders,” which involve the classified processing of orders received through their chain of command to launch a missile. These written tests are in addition to two other types of monthly testing on the missile system and on launch codes.

According to James and Wilson, the monthly tests all cover the same course material, but until now each base developed its own individual questions. As a result of the scandal, Wilson said the tests will now be developed by 20th Air Force.